The present invention relates to a material for a barrier film formed on a resist film for use in fabrication process or the like for semiconductor devices and a pattern formation method using the same.
In accordance with the increased degree of integration of semiconductor integrated circuits and downsizing of semiconductor devices, there are increasing demands for further rapid development of lithography technique. Currently, pattern formation is carried out through photolithography using exposing light of a mercury lamp, KrF excimer laser, ArF excimer laser or the like. Furthermore, use of F2 laser lasing at a shorter wavelength has been examined, but since there are a large number of problems in exposure systems and resist materials, the development in the use of the F2 laser is now being suspended.
In these circumstances, immersion lithography has been recently proposed for realizing further refinement of patterns by using conventional exposing light (for example, see M. Switkes and M. Rothschild, “Immersion lithography at 157 nm”, J. Vac. Sci. Technol., Vol. B19, p. 2353 (2001)).
In the immersion lithography, a region in an exposure system sandwiched between a projection lens and a resist film formed on a wafer is filled with a liquid (an immersion solution) having a refractive index n (whereas n>1) and therefore, the NA (the numerical aperture) of the exposure system has a value n·NA. As a result, the resolution of the resist film can be improved. Also, use of an acidic solution as the immersion solution has been recently proposed for further improving the refractive index of the liquid (see, for example, B. W. Smith, A. Bourov, Y. Fan, L. Zavyalova, N. Lafferty, F. Cropanese, “Approaching the numerical aperture of water—Immersion Lithography at 193 nm”, Proc. SPIE, Vol. 5377, p. 273 (2004)).
Now, a conventional pattern formation method employing the immersion lithography will be described with reference to FIGS. 12A through 12D, 13A and 13B.
First, a positive resist material having the following composition is prepared:
Base polymer: poly((norbornene-5-methylene-t-butylcarboxylate) (50 mol %)-(maleic anhydride) (50 mol %)) . . . 2 g
Acid generator: triphenylsulfonium trifluoromethane sulfonate . . . 0.05 g
Quencher: triethanolamine . . . 0.002 g
Solvent: propylene glycol monomethyl ether acetate . . . 20 g
Next, as shown in FIG. 12A, the aforementioned resist material is applied on a substrate 601 so as to form a resist film 602 with a thickness of 0.35 μm.
Then, as shown in FIG. 12B, by using a barrier film material having the following composition, a barrier film 603 is formed on the resist film 602:
Base polymer: polyvinyl hexafluoroisopropyl alcohol . . . 1 g
Solvent: n-butyl alcohol . . . 20 g
Next, as shown in FIG. 12C, the resultant barrier film 603 is annealed with a hot plate at a temperature of 120° C. for 90 seconds, so as to improve the denseness of the barrier film 603.
Then, as shown in FIG. 12D, with an immersion liquid 605 of water provided on the annealed barrier film 603 by, for example, a puddle method, pattern exposure is carried out by irradiating the resist film 602 through the barrier film 603 with exposing light 607 of ArF excimer laser with NA of 0.68 having passed through a mask 606.
After the pattern exposure, as shown in FIG. 13A, the resist film 602 is baked with a hot plate at a temperature of 105° C. for 60 seconds (post exposure bake).
Next, the barrier film 603 is removed by using a 2.38 wt % tetramethylammonium hydroxide aqueous solution (an alkaline developer) and the resultant resist film is developed. In this manner, a resist pattern 602a made of an unexposed portion of the resist film 602 and having a line width of 0.09 μm is formed as shown in FIG. 13B.
However, as shown in FIG. 13B, the resist pattern 602a obtained by the conventional pattern formation method is in a defective shape.
The present inventors have variously examined the reason why the resist pattern formed by the conventional immersion lithography is in a defective shape, resulting in finding the following: In the case where the barrier film 603 cannot be sufficiently dissolved in a developer such as an alkaline aqueous solution, the development of the resist film 602 is inhibited and hence the resist film 602 cannot be uniformly developed. As a result, the resist pattern is formed in a defective shape.
When the resist pattern 602a in such a defective shape is used for etching a target film, the resultant pattern of the target film is also in a defective shape, which disadvantageously lowers the productivity and the yield in the fabrication process for semiconductor devices.